A device of this type is disclosed by U.S. Pat. No. 5,660,519. According to the latter, the scanning device of the pick-and-place head in each case includes a row of transmitting and receiving diodes, which form a scanning plane perpendicular to the lifting direction at the height of the component located in the transporting position. While the pick-and-place head is traveling to the placement location on the substrate, the side contours of the component can be scanned by rotating the suction pick-up about the lifting axis, which allows the positional deviation of the center of the component from the pick-up axis to be ascertained. The presence or absence of the component on the pick-up is detected during the picking-up or placing of the component by sensing the suction pressure at the pipette. It goes without saying that the presence or absence of the component can also be established by optical measurement.
Furthermore, JP 11-154797 A discloses a pick-and-place device with a fixed turntable rotating step by step, under which a printed circuit board can be made to travel in two coordinate directions. The turret-like turntable is equipped with a multiplicity of pick-ups for the components, which run step by step through different stations and which transport the components from a pick-up position to an opposite placement position. Before the picking up, the free end of the pick-up runs through a control station with a perpendicular row of optical transmitting and receiving diodes in the manner of light barriers, whereby the position in height of the underside of the pick-up can be ascertained.
After the picking-up of the component, the end of the pick-up with the component runs through a further optical control station with a perpendicular row of diodes, whereby the position in height of the underside of the component, and consequently its overall height, can be ascertained. In the case of a pick-and-place head which can be made to travel in two coordinate directions, the pick-up would have to run through the fixed control station before and after picking up the component to allow a corresponding measurement to be carried out, which would generally involve an unacceptable detour between the pick-up position and the and the placement position, and vice versa.
Furthermore, it is known, for example from U.S. Pat. No. 4,875,285, to design the pick-and-place head in the manner of a turret with a multiplicity of suction pick-ups arranged in a circular manner on a rotor, a stator having with processing stations for the components arranged along the circulatory path of the pick-ups, which components are centered, contacted and electrically, optically or mechanically measured in these stations, for example according to column 2, line 65 et seq. It is currently generally customary to carry out the positional determination of the components on the pick-up by a CCT camera, which measures the placement side of the components, in particular the position of the contact areas, in reflected light. The angular position of the component can be corrected in a downstream rotating station. The x-y offset is taken into account by corresponding correction of the target coordinates of the pick-and-place head.
Furthermore, WO 9949713 A discloses a turret pick-and-place head with a stator and a rotor, which is provided with pick-ups for the components arranged in a circulatory manner. A line sensor is arranged on the stator outside a lower placement station between two holding stations for the pick-ups into the and aligned in relation to the axis of rotation of the rotor. The components sliding past, adhering to the pick-up, can be identified from the obscuration of the sensor. Since the pick-up has to be moved into the sensing range of the sensor, it cannot be checked in a direct time-related manner with the picking-up operation. Since the light directed onto the line sensor cannot be exactly focused, adequately sharp projection is not possible, in particular for highly miniaturized components. Sharp optical focusing is possible only in the case of a singular scanning beam, for example of a laser light barrier.
The current trend toward ever smaller components, of for example an edge length of 0.25 mm, requires a very narrow suction channel in the pick-up, which makes it difficult for the vacuum to be sensed, in particular when there is soiling. Furthermore, inaccuracies of the pick-up position may occur if the component does not completely cover the suction channel and, as a result of this leakage, the result of the vacuum scanning is unreliable. For example, in the case of a turret head, under some circumstances the absence of a component is consequently only noticed in the optics station during the placement phase. The picking up of a replacement component requires a considerable additional amount of time to be expended.